Molecular-based imaging provides unique opportunities to assess the pharmacokinetics and targeting properties of r potential therapeutic agents, as well as to assess vital cellular processes in vivo. The ability to monitor the molecular processes of cancer through non-invasive imaging may provide critical information regarding the effects of therapy. In the context of pre-clinical research, the use of in vivo imaging permits the acquisition of a complete dynamic biodistribution study of a molecular tracer on an single animal, thereby reducing the number of animals required to reach a statistically adequate result. Often the imaging techniques and targeting agents that are tested in small animal imaging modalities are directly transferable to the clinical setting. The Small Animal Imaging Core (SAIC) is a shared resource dedicated to providing investigators access to state of the art small animal imaging capabilities for use in basic and translational research relevant to the mission of the City of Hope Cancer Center. Specific aims of the SAIC include: (1) keeping abreast of the latest developments, current capabilities, and limitations of small animal imaging as pertains to cancer research; (2) implementing, developing, calibrating, maintaining, and operating relevant imaging systems within the context of a small animal imaging laboratory; and (3) optimizing the use of small animal imaging in research at City of Hope in collaboration with investigators. Core personnel currently include a Director, an imaging physicist, and a manager, all of whom are highly experienced in the use of imaging for research with animals. Small animal imaging systems in operation include two units for bioluminescence optical imaging (one has been modified for fluorescence imaging [IVIS 100, Caliper Life Sciences]); a gamma camera (y- IMAGER, Biospace, Inc.); a PET scanner (microPET R4, Siemens); and a CT scanner (microCAT II Hi Res, Siemens). The microPET and microCAT are readily used in tandem to generate co-registered functional anatomic PET/CT images. The Animal Resources Center has provided three rooms within the Parvin Biomedical Research Building for use by the SAIC (one room for the microPET, microCAT, and the y- IMAGER, and two rooms for the IVIS optical imaging instruments. A system has been developed for monitoring instrument usage and to bill users for a portion of the costs of the imaging procedures.